1. Field of the Invention
The present invention relates to an electrophotographic printer which takes account of exhaust gas regulations.
2. Description of the Prior Art
A conventional electrophotographic printer is described with reference to FIGS. 4 and 5. In FIG. 4, paper which is fed from a paper feed roller 1 passes through a drive roller 2, a paper transfer roller 3 and image carriers 4a to 4d. Four rollers of said image carriers are disposed in the order of color of blue 4a, red 4b, yellow 4c and black 4d, respectively. A printed paper then passes through a paper transfer roller 6, is heated for fixing by a fixing roller 7 and enters a paper delivery portion 9. During this operation, a large amount of solvent gas comes out of the fixing roller 7, hence it is discharged by a blower 15 through an exhaust gas port 8. Numerals 10a to 10d designate liquid developer tanks for blue, red, yellow and black colors, respectively, and numeral 11 designates a casing.
Next, a printing portion is described by use of FIG. 5. As a prior art, there are disclosed various kinds of method and apparatus for obtaining images by use of an electrophotographic method using a liquid toner, and most widely known is that shown in FIG. 5 in which an electrostatic latent image 29 formed on a surface of an image carrier 4 (4a to 4d) is applied by a liquid developer 24 by use of a developing device 23 so as to form a toner image 25, a surplus liquid of the toner image 25 is removed by a squeezing device 26, then a transfer charging of a reverse polarity with the toner is made by a transfer device 28 from a back side of a transfer material 27 so that a transfer is made. Incidentally, numeral 40 designates a light exposing device, numeral 41 designates an electrostatic charger, numeral 42 designates a static eliminator and numeral 43 designates a cleaning blade.
Solvent which is generally used in said conventional apparatus is an isoparaffin solvent of a carbon number of 10 or more, which is for example Isopar L.M. etc. of Exxon Chemical Company. While at present in Japan there is no specific regulation as to an exhaust gas containing these solvents, there are regulations in the United Kingdom to limit VOC (volatile organic compound) regarding a printing machine to 150 mg/m.sup.3, which is extremely strict. This must be taken account of for a case not only of an international trade but also of future possible regulations in Japan.
As a solvent treatment method, there are ones including an atmospheric emission, a catalytic combustion, an active carbon adsorption and a condensation by cooling. Said respective solvent treatment method, however, has following problems:
1 In case of an atmospheric emission, when an amount of use of Isopar L, for example, in a printing machine is 8.64 kg/hr, as the explosion lower limit of concentration of Isopar L is 0.6 to 0.7 volume % (44.732-52.185 mg/m.sup.3 N), it is so obligated that handling thereof is normally to be made with a concentration of 1/3 or less of said limit. So, if an objective concentration is set to 0.22 volume % (16.402 mg/m.sup.3 N), a blower capacity becomes 527 m.sup.3 /hr due to requirement for increasing air volume to be mixed. In this case, the concentration of Isopar L in the gas to be emitted is 16.402 mg/m.sup.3 N, which may by no means satisfy said regulation in Europe. PA0 2 In the method of catalytic combustion, hydrocarbon is converted into carbon dioxide and water at a temperature of about 400.degree. C., hence recovery of solvent becomes impossible. Further, as a high temperature combustion gas is discharged as an exhaust gas, the apparatus cannot be installed in an office room. PA0 3 In the method of active carbon adsorption, while hydrocarbon is well adsorbed by active carbon, solvent used in an electrophotographic printer of a carbon number of 10 or more, if it is once adsorbed, cannot be desorbed by use of a hot air but requires a high temperature steam. In a usual office room, there is not such a large steam source, and if a small boiler is used, there is a disadvantage that a treatment device becomes large. PA0 4 In the case of concentration by cooling, as the temperature of gas containing a solvent is lowered, the solvent gas concentration in the gas is also lowered, but in order to attain a concentration of 150 mg/m.sup.3 or less, there is a problem as follows: that is, in order to make the concentration of Isopar L to a level of 150 mg/m.sup.3 with an aim to satisfy 150 mg/m.sup.3 as an outlet concentration of the exhaust gas; it is necessary to make cooling to a temperature of -7.2.degree. C. in relation to vapor pressure. However, there is a problem for maintaining a continuously flowing gas in a range of temperature under 0.degree. C. There occurring a sticking of frost to a cooling portion, it is difficult to maintain the gas at a temperature of -7.2.degree. C. continuously.
In order to dilute said Isopar L of 8.64 kg/hr to 150 mg/m.sup.3 by use of air only in the case of atmospheric emission, there is a need to use a blower of a capacity of 57.600 m.sup.3 /hr, which, being too large, is inappropriate for use in an office room etc.